In the related art, semiconductor light sources are used as the light sources in liquid crystal projectors and so forth (for example, see Patent Literature 1). In Patent Literature 1, three types of fluorophores are irradiated with excitation light output from a single semiconductor light source, creating red, green, and blue fluorescence, and these three colors of fluorescence are used to reproduce colors in an image.
In applications such as microscopes, liquid crystal projectors, and the like, a comparatively small region is irradiated with illumination light from a light source. The apparatus in Patent Literature 1, being based on the Etendue principle, is not suitable for applications in which such a small region is illuminated.
In other words, Etendue, which is represented by the product of the cross-sectional area of the light beam and the solid angle of the light beam at a position in the optical system, is conserved from the light source to the irradiation position. Patent Literature 1 considers the arrangement of a plurality of light sources to improve the brightness of the illumination light. In that case, the light-emission area of the light source as a whole becomes large, and Etendue at the light source side becomes large. As a result, although the amount of light from the light source increases due to the increased light-emission area of the entire light source, Etendue at the light source side also increases, causing the light guiding efficiency to drop. In other words, it is not possible to efficiently guide all of the light emitted from the light source to a small illumination region at the irradiation position, and part of the light suffers from vignetting and thus does not contribute to an improvement in the brightness of the illumination region.